Introduced settings database based on sqlite

Potential replacement for QSettings. This database will allow us to save
settings incrementially, removing most of the performance issues we're
having when our few megabytes of settings are being saved.

Not done in the form of a QSettings backend because it doesn't seem the
backends can do an incremental update of the settings.

Currently used by the QuickOpenPlugin for testing.

src/plugins/coreplugin/settingsdatabase.h

@@ -0,0 +1,70 @@
+/**************************************************************************
+**
+** This file is part of Qt Creator
+**
+** Copyright (c) 2009 Nokia Corporation and/or its subsidiary(-ies).
+**
+** Contact:  Qt Software Information (qt-info@nokia.com)
+**
+** Commercial Usage
+**
+** Licensees holding valid Qt Commercial licenses may use this file in
+** accordance with the Qt Commercial License Agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and Nokia.
+**
+** GNU Lesser General Public License Usage
+**
+** Alternatively, this file may be used under the terms of the GNU Lesser
+** General Public License version 2.1 as published by the Free Software
+** Foundation and appearing in the file LICENSE.LGPL included in the
+** packaging of this file.  Please review the following information to
+** ensure the GNU Lesser General Public License version 2.1 requirements
+** will be met: http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html.
+**
+** If you are unsure which license is appropriate for your use, please
+** contact the sales department at qt-sales@nokia.com.
+**
+**************************************************************************/
+
+#ifndef SETTINGSDATABASE_H
+#define SETTINGSDATABASE_H
+
+#include "core_global.h"
+
+#include <QtCore/QObject>
+#include <QtCore/QString>
+#include <QtCore/QStringList>
+#include <QtCore/QVariant>
+
+namespace Core {
+
+namespace Internal {
+class SettingsDatabasePrivate;
+}
+
+class CORE_EXPORT SettingsDatabase : public QObject
+{
+public:
+    SettingsDatabase(const QString &path, const QString &application, QObject *parent = 0);
+    ~SettingsDatabase();
+
+    void setValue(const QString &key, const QVariant &value);
+    QVariant value(const QString &key, const QVariant &defaultValue = QVariant()) const;
+    bool contains(const QString &key) const;
+    void remove(const QString &key);
+
+    void beginGroup(const QString &prefix);
+    void endGroup();
+    QString group() const;
+    QStringList childKeys() const;
+
+    void sync();
+
+private:
+    Internal::SettingsDatabasePrivate *d;
+};
+
+} // namespace Core
+
+#endif // SETTINGSDATABASE_H